When a hand-held power drill is being used in the vicinity of electric power conductors, there is a danger of personal injury due to contact between the drill and a live conductor, as well as a possibility of fire and damage to the wiring. These problems are particularly likely to occur when drilling through building walls, because the exact positions of electrical cables serving power outlets, lighting, etc., are usually unknown.
There is no easy way to determine the exact location of hidden wires, and consequently, drilling through insulated wiring is a common occurrence, and often requires removal of large parts of walls and rewiring.